This invention relates generally to an optical fluid level sensor, and more particularly, to an optical fuel level sensor capable of providing fuel level and calibration information via electronic signals.
Various types of fuel level sensors have been employed for the purpose of providing fuel level information, particularly in the automotive industry. One such fuel level sensor involves a light conducting waveguide having a photo source and photo receiver, wherein light emanates from the photo source and impinges upon a series of tiered facets located at various depths within the tank. Those facets located above the current fuel level inwardly reflect the light so that it is returned to the photo receiver, while those facets located below the current fuel level outwardly refract the light such that it is never received by the photo receiver. Thus, the sensor is capable of generating an electronic signal representative of the amount of light received by the photo receiver, wherein the amount of light received corresponds to a particular fuel level.
One problem associated with these optical fuel level sensors is that they may experience a long-term drift, or measurement shift, that impacts the accuracy and stability of the sensor""s readings. Changes to the photo source output, photo receiver input, or other associated circuitry could be incorrectly interpreted as a change in fuel level. Such a phenomenon is not uncommon for sensor components, and the drifting is typically accelerated by exposure to extreme temperatures and other harsh environmental conditions.
Furthermore, optical fuel level sensor designs such as those discussed above, typically utilize a photo source and receiver located at one axial end of the waveguide. Locating the photo source and receiver at either the very top or the very bottom of the waveguide increases the distance that light must travel, particularly when the fuel tank is completely empty or completely full. For example, when the fuel tank is empty, optical fuel level sensors having photo sources and receivers located at their upper most axial end must emit light from the top of the waveguide such that it travels the entire length of the waveguide, reflects off a dry facet located near the waveguide""s lowermost end, and then travels back up the length of the waveguide to the photo receiver. Thus, the light has traveled a total distance roughly equivalent to twice the axial length of the waveguide. The greater the distance that light must travel, the greater the opportunity for signal loss, which can cause the photo receiver to report inaccurate readings.
Therefore, it is a general object of the present invention to provide an optical fuel level sensor that minimizes the effects of long-term drift and signal loss. Features aimed at minimizing those effects may include one or more of the following: a calibration feature, a center mounted photo source and receiver, and an optical fuel level sensor having two tapered axial ends.
The above noted shortcomings of prior art fuel level sensors are overcome by the present invention which provides an optical fluid level sensor for use with a fluid vessel, comprising a waveguide, a photo source, and a photo receiver. The waveguide is capable of conducting light and has an outer periphery that includes a plurality of tiered facets, each facet is capable of both reflecting light internally within the waveguide and refracting light out of the waveguide depending upon whether or not fluid is in contact with that facet. The waveguide also includes a calibration feature located at a predetermined position. The photo source emits light into the waveguide and the photo receiver receives light exiting the waveguide. The optical fluid level sensor uses the light received by the photo receiver to provide an electronic fluid level signal representative of a fluid level within the vessel, and the sensor further provides calibration information in an electronic signal that identifies when the fluid level reaches the predetermined position. This fluid level sensor can also be implemented as part of a fuel level sensing system to be used with a fuel tank. In addition to the optical sensor, the fuel level sensing system includes a power source having an output for providing a power signal and an interface electronics unit. The interface electronics unit includes a signal input for receiving the electronic fuel level signal and is coupled to the sensor for receiving the calibration information. Furthermore, the interface electronics unit utilizes the fuel level signal to determine the fuel level within the fuel tank, and utilizes the calibration information to calibrate the sensor with respect to the predetermined position.
In accordance with yet another aspect of the present invention, there is provided an optical fluid level sensor for use with a fluid vessel, the sensor comprises a waveguide, a photo source, and a photo receiver. The waveguide conducts light and has a tapered first axial end, a tapered second axial end, and an outer periphery that includes a plurality of tiered facets. Each of the tiered facets reflects light internally within the waveguide and refracts light out of the waveguide according to the presence of fluid against the tiered facet. The photo source is located at a position approximately equidistant from the first and second axial ends and emits light into the waveguide in a first direction generally towards the first axial end and in a second direction generally towards the second axial end. Similarly, the photo receiver is located at a position approximately equidistant from the first and second axial ends and receives light from within the waveguide from the first and second directions. The sensor utilizes the light received by the photo receiver to provide an electronic fluid level signal representative of a fluid level within the vessel. This fluid level sensor can also be implemented as part of a fuel level sensing system to be used with a fuel tank. In addition to the optical sensor, the fuel level sensing system includes a power source for providing a power signal and an interface electronics unit for receiving a fuel level signal from the optical sensor. The sensor utilizes the light received by the photo receiver from the first and second directions to provide the interface electronics unit with the fuel level signal which the interface electronics unit utilizes to determine the fuel level within the fuel tank.
An advantage of this invention is that it provides an optical fuel level sensor which can offset the affects of long term drift of sensor components through the use of a calibration feature. Also, the accuracy of the sensor is increased and the size can be decreased by utilizing a dual-tapered waveguide design having a photo source and receiver mounted near the center of the waveguide. Thus, the optical fuel level sensor of the present invention can be made more accurate and economical to manufacture than other designs that provide fuel level sensing.